CN101542147B - Ball spline device - Google Patents

Abstract

A nut member (2) has, on an inner peripheral surface facing a spline shaft (1), a track groove (30) in which balls (3) circulate, the track groove being composed of a load linear groove (31) formed so as to face the ball rolling grooves (10a, 10b) of the spline shaft, an unloaded linear groove (32) provided in parallel with the load linear groove, and a pair of ball deflection grooves (33) which connect the load linear groove and the unloaded linear groove to each other and move the balls (3) between them, the ball deflection grooves (33) forcibly changing the traveling direction of the balls (3) rolling in the ball rolling grooves (10a, 10b), and the balls (3) being separated from the ball rolling grooves (10a, 10b) by the profile of the spline shaft (1). A ball guide surface (11) is formed on one side of the ball rolling grooves (10a, 10b) of the spline shaft (1) at a position facing the ball deflection groove (33) of the nut member (2), and the ball guide surface smoothly continues to the ball rolling grooves (10a, 10 b).

Description

Ball spline device

technical field

The present invention relates to a ball spline device that freely combines a spline shaft and a nut member through relative linear motion of a plurality of balls, and is used in linear guides of machine tools and various industrial machines, transmission parts of industrial robots, and the like. the

Background technique

Conventionally, as such a ball spline device, devices disclosed in JP-A-61-179414 and JP-A-58-137616 are known. These ball spline devices are composed of a spline shaft with a plurality of ball rolling grooves extending in the longitudinal direction, and a nut member which is mounted on the spline shaft via a plurality of balls and has an infinite circulation path for the balls, and is accompanied by balls. The infinite loop of the above-mentioned nut member can move freely around the spline shaft along its length direction. the

In addition, in the infinite circulation path of the balls provided on the nut member, the load path in which the balls roll while carrying the load acting between the nut member and the spline shaft, the ball return path formed in parallel with the load path, and the connection These load passages and the U-shaped direction change passage of the ball return passage are constituted. Furthermore, by arranging the above-mentioned direction change path at both ends of the load path and the ball return path, an infinite circulation path for the balls can be formed. the

If the ball return path is formed through the nut member itself, such a nut member tends to have a larger diameter due to thicker walls, and when the diameter of the ball is small, the diameter of the ball return hole also becomes a small diameter, It is difficult to form the ball return hole directly through the nut member. Therefore, in the ball spline device shown in the above document, a cage made of synthetic resin is interposed between the inner peripheral surface of the cylindrical nut member and the spline shaft passing through it, The ball return path and the direction change path are formed by such cooperation of the cage and the nut member. the

In addition, in order for the balls rolling on the above-mentioned load passage to move to the ball return passage through direction change, it is necessary to disengage such balls from the ball rolling groove of the spline shaft. Therefore, in the conventional ball spline device, a ball rising portion continuous with the direction changing path is provided with respect to the cage, and the balls rolling in the ball rolling groove ride on the rising portion and come off the lifting portion. The ball rolling groove is accommodated in the direction changing path formed jointly by the cage and the nut member. Patent Document 1: Japanese Patent Application Publication No. 61-179414 Patent Document 2: Japanese Patent Application Publication No. 58-137616

Contents of the invention

The problem to be solved by the invention

However, in the conventional ball spline device as already described, since the ball return passage is formed jointly by the retainer and the nut member, such a ball return passage has to be at least part of the thickness of the retainer from the spline axial direction. Its radial direction separates. In addition, the above-mentioned direction change path and ball return path are formed on the cage, and in order to realize its complicated shape, it is produced by injection molding of synthetic resin, but if the cage mounted on the inner peripheral surface of the nut member is deformed, due to Such a retainer is in contact with the spline shaft, and movement of the nut member is hindered, so it is difficult to form the retainer extremely thin. Therefore, in the conventional ball spline device in which the retainer is accommodated between the spline shaft and the nut member, the outer diameter of the nut member is affected by the thickness of the retainer, and there is a limit to miniaturization of the nut member. the

In addition, in the conventional ball spline device, the ball is detached from the ball rolling groove of the spline shaft by using the raised portion of the cage. Directly above the groove, the direction changing path enters from there, so correspondingly, a space is required between the nut member and the spline shaft, and this is also a major factor hindering the miniaturization of the nut member. the

In addition, in the conventional ball spline device, since the retainer is required, and the raised portion of the retainer needs to be correctly positioned relative to the ball rolling groove, it takes man-hours to manufacture and assemble, and there is a relative assembly accuracy. Vulnerable reliability in terms of problems. To solve the problem means

The present invention has been made in view of such a problem, and its object is to provide a nut member that can make the outer diameter of the nut member miniaturized to the limit while fully exerting the original function, and can be assembled easily and cheaply. Ball spline device that maintains reliability while being easy to manufacture. the

In order to achieve the above object, the ball spline device of the present invention is composed of a spline shaft and a nut member. The spline shaft has a ball rolling groove formed in the axial direction on the outer peripheral surface. The nut member is formed so that the spline shaft penetrates The substantially cylindrical shape is assembled on the above-mentioned spline shaft through a plurality of balls, and at the same time, there is a track groove in which the above-mentioned balls circulate on the inner peripheral surface facing the above-mentioned spline shaft. the

The above-mentioned track groove is composed of a load linear groove, an unloaded linear groove, and a pair of ball deflection grooves. The above-mentioned load linear groove is a load linear groove formed opposite to the ball rolling groove of the spline shaft, and forms the load path of the ball; the above-mentioned The unloaded linear grooves are provided parallel to the loaded linear grooves, and at the same time, open toward the outer peripheral surface of the spline shaft; the above-mentioned pair of ball deflection grooves connect these loaded linear grooves and the unloaded linear grooves in communication, and the balls reciprocate between them. , At the same time, open to the outer peripheral surface of the above-mentioned spline shaft. the

That is, the ball spline device of the present invention does not have a cage between the spline shaft and the nut member, the balls circulate in the track groove formed on the inner peripheral surface of the nut member, between loads. Among the load linear grooves, unloaded linear grooves, and ball deflection grooves that constitute the above-mentioned track grooves, since the load linear grooves face the ball rolling grooves of the spline shaft and constitute the load passages of the balls, such load linear grooves are of course directed towards the spline shaft. The key shaft is open, and other unloaded linear grooves and ball deflecting grooves are also open to the outer peripheral surface of the spline shaft. Balls roll in the above-mentioned unloaded linear grooves and ball deflecting grooves while facing the spline shaft. the

Therefore, the infinite circulation path of the ball is formed in a state of being in contact with the outer peripheral surface of the spline shaft. Compared with the conventional ball spline device equipped with a cage, as long as the diameter of the spline shaft is the same, it is possible to The outer diameter of the nut member is reduced. This makes it possible to miniaturize various industrial machines using the ball spline device. From another point of view, when the outer diameter of the nut member that can be used in various industrial machines is fixed, the present invention Compared with existing products, the ball spline device can use a spline shaft with a larger diameter, which can improve the movement accuracy of the nut member with the rigidity of the spline shaft, and realize the improvement of the transmission torque, which can contribute to the adoption of the ball spline. The capability of the industrial machinery of the key device is improved. the

On the other hand, in the ball spline device of the present invention, the ball deflection groove is configured in such a manner that the traveling direction of the balls rolling in the ball rolling groove of the spline shaft is forcibly changed, and the spline The profile of the shaft allows the balls to escape from the ball rolling grooves, and on the other hand, the separated balls are guided to the above-mentioned unloaded linear grooves together with the outer peripheral surface of the ball rolling grooves. the

That is, in the present invention, when the balls are separated from the ball rolling grooves of the spline shaft, instead of using the conventional structure in which the balls are lifted up to directly above the ball rolling grooves by the lifting portion, splines are used. The outline of the key shaft. The direction of travel of the balls rolling in the ball rolling groove is forcibly changed by the ball deflecting groove opened to the spline shaft, and the ball follows the contour of the spline shaft out of the ball rolling groove, and is deflected by the outer peripheral surface of the spline shaft and the ball deflection shaft. Induces toward the unloaded linear groove while restricting the rolling direction. the

In this way, in the ball spline device of the present invention in which the balls are separated from the ball rolling grooves of the spline shaft, there is no need for a raised portion for raising the balls from the ball rolling grooves, and rolling such a raised portion relative to the balls is unnecessary. Since the man-hour for positioning the grooves is freed, it can be manufactured cheaply and easily. In addition, in the conventional raised portion, since the balls ride continuously, there is a risk of deformation and damage when the balls circulate at high speed. In the ball spline device of the present invention that does not use such a raised portion In this case, there is no such risk, and the reliability when the nut member is moved at high speed with respect to the spline shaft can be improved. the

Description of drawings

FIG. 1 is a partially exploded perspective view showing an embodiment of a ball spline device to which the present invention is applied. Fig. 2 is a sectional view perpendicular to the axial direction of the ball spline device shown in Fig. 1 . 3 is a diagram showing a state in which the track groove that the nut member has is developed on a plane. 4 is a cross-sectional view perpendicular to the axial direction of a nut main body constituting a nut member. Fig. 5 is a perspective view showing an end cap constituting a nut member. Fig. 6 is an enlarged view of the balls rotating in the track grooves viewed from the axial direction of the spline shaft. the

Detailed ways

Next, the ball spline device of the present invention will be described in detail with reference to the drawings. the

1 and 2 are diagrams showing an embodiment of a ball spline device to which the present invention is applied. This ball spline device is composed of a spline shaft 1 formed in a substantially cylindrical cross section and a nut member 2 assembled to the spline shaft 1 via a plurality of balls 3 while being formed in a substantially cylindrical shape. The nut member 2 is configured to be able to freely reciprocate in the axial direction around the spline shaft 1 . the

On the outer peripheral surface of the above-mentioned spline shaft 1, four ball rolling grooves 10 are formed in the axial direction, and the balls 3 roll on these ball rolling grooves 10, and at the same time, a load is carried between the nut member 2 and the spline shaft 1 . The shape of each ball rolling groove 10 in a cross section perpendicular to the longitudinal direction is formed in an arc shape, that is, a shape composed of a single arc with a curvature slightly larger than that of the spherical surface of the ball. These ball rolling grooves 10 are constituted by a ball rolling groove 10a that receives a load when the nut member 2 rotates in the direction of the arrow A around the spline shaft 1, and a ball rolling groove 10b that receives a load when it rotates in the direction of the arrow B. The adjacent ball rolling grooves 10 a and 10 b form a set, and a plurality of sets are formed at equal intervals on the outer peripheral surface of the spline shaft 1 . Therefore, torque can be transmitted between the nut member 2 and the spline shaft 1 . In the ball spline device shown in Figures 1 and 2, two sets of four ball rolling grooves 10 are formed on the outer peripheral surface of the spline shaft 1, but it is also possible to form three sets of six or four sets of eight ball rolling grooves. groove. the

On the other hand, the nut member 2 is composed of a metal nut body 4 and a pair of end caps 5 fastened to both axial ends of the nut body 4 by bolts. The through hole of the spline shaft 1. In addition, a keyway 40 is formed on the outer peripheral surface of the nut body 4 for use when the nut member 2 is mounted on a mechanical device. the

In this way, the nut member 2 constituted by the combination of the nut body and the end cover has a track groove 30 for endless circulation of balls on the inner peripheral surface facing the through hole of the spline shaft 1 . This track groove 30 is composed of a load linear groove 31 formed on the inner peripheral surface of the nut main body 4 facing the ball rolling groove 10 of the spline shaft 1 , and the load linear groove 31 is aligned with the inner peripheral surface of the nut main body 4 . The unloaded linear grooves 32 are formed in parallel at a slight interval, and the rolling direction of the balls 3 is switched 180 degrees between these loaded linear grooves 31 and the unloaded linear grooves 32, and the balls 3 are reciprocated between these grooves. The ball deflection groove 33 is formed. The entire track groove 30 is open toward the spline shaft 1 , and the balls 3 arranged in the track groove 30 circulate in the track groove 30 while facing the spline shaft 1 . the

FIG. 3 is a diagram showing a state in which the track groove 30 is developed on a plane. The load linear groove 31 constituting a part of the track groove 30 has a cross section perpendicular to the longitudinal direction, which is formed in an arc shape similarly to the ball rolling groove 10 on the spline shaft 1 side. Since four ball rolling grooves 10 are formed on the spline shaft 1, the direction in which the balls 3 contact each ball rolling groove 10 of the spline shaft 1 or each load linear groove 31 of the nut member 2 is the same as that of the spline shaft 1. In terms of the circumferential direction, it is different every 90 degrees. Thereby, the nut member 2 can reciprocate along the spline shaft 1 while bearing all the loads acting on the spline shaft 1 except in the axial direction. the

On the other hand, the unloaded linear groove 32 constituting a part of the above-mentioned track groove 30 is formed as a passage slightly larger than the diameter of the ball 3, and is formed in the nut member in a state of opening toward the outer peripheral surface of the spline shaft 1. on the inner peripheral surface. Therefore, the ball 3 can be accommodated in the unloaded linear groove 32 in a no-load state, that is, in a state where free rotation is maintained. In addition, since the unloaded linear groove 32 is opened toward the spline shaft 1 , the ball 3 can rotate inside the unloaded linear groove 32 while being in contact with the spline shaft 1 . the

In addition, the above-mentioned ball deflection groove 33 is constituted in such a manner that it has a substantially U-shaped track connecting the load linear groove 31 and the unloaded linear groove 32, and allows the ball to roll in the load linear groove 31 while carrying a load. The ball 3 is released from the load, and at the same time, the rolling direction of the ball 3 is gradually changed and the direction is changed by 180 degrees, and it is sent into the above-mentioned unloaded linear groove 32. The ball deflection groove 33 is formed so that it is the shallowest at the connection portion with the load linear groove 31 and is the deepest at the connection portion with the unloaded linear groove 32 . As the ball deflecting groove 33 gradually becomes deeper, if the ball 3 rolling on the load linear groove 31 enters the ball deflecting groove 33, such a ball 3 is released from the load and becomes in the ball deflecting groove in a no-load state. 33 advances toward the unloaded linear groove 32, and enters in the unloaded linear groove 32 under the state that this state does not change. the

When the nut member 2 is moved along the spline shaft 1, the balls 3 sandwiched between the ball rolling grooves 10 of the spline shaft 1 and the load linear grooves 31 of the nut member 2 are moved by the movement of the nut member 2 relative to the spline shaft 1. The speed 0.5V which is half of the moving speed V moves in the load linear groove 31 . When the balls 3 rolling in the load linear groove 31 reach the ball deflecting groove 33, as described above, since the depth of the ball deflecting groove 33 gradually becomes deeper, they are gradually released from the load. The ball 3 released from the load is pushed by the subsequent ball 3 and travels in the ball rolling groove 10 of the spline shaft 1 while being pushed, but since the ball deflection groove 33 blocks the ball rolling groove The rolling of the ball 3 in 10 forcibly changes the traveling direction of the ball 3, so the ball 3 moves from the ball deflection groove 33 to one side of the ball rolling groove 10, and travels along the outline (shape) of the spline shaft 1 until climbing to the outer peripheral surface of the spline shaft. As a result, the balls 3 are completely separated from the ball rolling grooves 10 of the spline shaft 1 and completely accommodated in the ball deflection grooves 33 of the nut member 2 . the

Since the ball deflecting groove 33 developed on a flat surface has a substantially U-shaped track, the ball 3 accommodated in such a ball deflecting groove 33 enters so that its rolling direction is reversed and faces the outer peripheral surface of the spline shaft 1. In the unloaded linear groove 32 of the nut member 2. In addition, the balls 3 traveling in the unloaded linear groove 32 enter the ball deflection groove 33 on the opposite side, and after reversing the rolling direction, enter the ball rolling groove 10 of the spline shaft 1 and the load of the nut member 2. Between the straight grooves 31. At this time, the balls 3 travel along the contour (shape) of the spline shaft and enter the ball rolling grooves 10, and as the ball deflection grooves 33 gradually become shallower, the state transitions from the no-load state to the load-bearing state. the

The ball 3 circulates in the track groove 30 of the moving part 2 like this, and along with this, the nut member 2 can move continuously along the spline shaft 1 without interruption. the

Of the load linear grooves 31, unloaded linear grooves 32, and ball deflection grooves 33 constituting the track groove 30, the loaded linear grooves 31 and the unloaded linear grooves 32 are formed on the inner peripheral surface of the through hole of the nut body 4. , FIG. 4 is a diagram showing a cross-section of the nut body 4 perpendicular to the axial direction, and the cross-sectional shape is continuous in the axial direction of the nut body 4 . The shape of the inner peripheral surface of the nut main body 4 also includes the above-mentioned loaded linear groove 31 and unloaded linear groove 32, which are formed by wire-cut electric discharge machining. The load linear groove 31 may be subjected to grinding or the like after the wire-cut electric discharge machining in order to improve the surface roughness. However, when the inner diameter of the through hole of the nut main body 4 is large, the above-mentioned load straight line may be formed by cutting or grinding on the circumferential nut main body 4 having a uniform inner peripheral surface without using wire-cut electrical discharge machining. Groove 31 and unloaded linear groove 32. the

On the other hand, a ball deflection groove 33 constituting the track groove 30 is formed on the above-mentioned end cover. FIG. 5 is a perspective view of the end cap 5 viewed from the nut main body 4 side. A U-shaped ball deflection groove 33 is formed on the inner peripheral surface of the through hole of the end cover 5, and a seal protrusion 50 is formed facing the ball rolling groove 10 of the spline shaft 1 through a slight gap. In addition, an inlet groove 51 continuous with the key groove 40 of the nut body 4 is formed on the outer peripheral surface of the end cover 5, so that the key can be released from the keyway of the nut member 2 even when the end cover 5 is fixed to the nut body 4. Axially slide into the keyway 40 of the nut body 4 . Furthermore, on this end cover 5, a support post 52 for positioning the nut main body 4 is protruded. The ball deflection groove 33 on the side of the end cover 5 and the load linear groove 31 and the unloaded linear groove 32 on the side of the nut main body 4 can be correctly combined. the

Since the above-mentioned end cap 5 has a complex shape, it is produced by injection molding of synthetic resin. As another manufacturing method, metal injection molding (MIM molding) can also be used. In addition, if the outer diameter of the spline shaft is large and the end cover is also enlarged, it may be formed by cutting. the

In addition, in FIG. 1, although the nut member 2 is constituted by the combination of the nut main body 4 and the end cover 5, this is because, when the outer diameter of the spline shaft 1 is small, the balls will be removed by cutting or grinding. It is difficult to form the deflecting groove 33 on the inner peripheral surface of the nut member 2, but if the outer diameter of the spline shaft 1 is sufficiently large, it is easy to form the ball deflecting groove 33 on the inner peripheral surface of the nut member 2 by cutting or grinding. If so, the above-mentioned nut member 2 can also be made of a single metal material.

FIG. 6 is an enlarged view of the ball 3 rotating in the track groove 30 viewed from the axial direction of the spline shaft 1 . A flat ball guiding surface 11 adjacent to each ball rolling groove 10 is formed on the spline shaft 1 . The ball guiding surface 11 is provided on one side of the ball rolling groove 10 to face the ball deflecting groove 33 provided in the nut member 2, and is formed along the tangential direction of the arcuately formed ball rolling groove 10. Furthermore, the end portion of the ball guiding surface 11 on the opposite side to the ball rolling groove 10 is continuous with the outer peripheral surface 12 of the spline shaft 1 formed with a constant curvature. the

Such a ball guiding surface 11 can be ground simultaneously with the spline shaft 1 and the ball rolling groove 10 by using a forming grinding wheel, and as a result, the continuity between the ball guiding surface 11 and the ball rolling groove 10 can be significantly improved. the

By forming the ball guiding surface 11 that is smoothly continuous with the ball rolling groove 10, the ball 3 that is blocked from rolling in the ball rolling groove 10 of the spline shaft 1 by the ball deflection groove 33 is changed along the above-mentioned direction while its traveling direction is changed. The ball guiding surface 11 escapes from the ball rolling groove 10 and will reach the outer peripheral surface 12 of the spline shaft 1 . Then, while rolling in the ball deflection groove 33 , it enters the unloaded linear groove 32 along the outer peripheral surface 12 of the spline shaft 1 . The one-dot chain line in FIG. 6 represents the rotation track L of the ball 3 in the ball deflection groove 33 . Because the ball 3 is in contact with the above-mentioned ball guiding surface 11 and the outer peripheral surface 12 of the spline shaft 1 between the load linear groove 31 and the unloaded linear groove 32, that is, inside the ball deflection groove 33, and at the same time, moves along them, so as shown in the figure As shown, the locus L of the ball 3 in the ball deflecting groove 33 is projected onto the spline shaft 1 on the cross section perpendicular to the axial direction, and becomes the spline shaft in the portion facing the ball deflecting groove 33 . 1 contour (shape) consistent with the locus. the

Therefore, since the infinite circulation path of the balls 3 provided in the nut member 2 is as close as possible to the spline shaft 1, when the nut member 2 is provided with the infinite circulation path of the balls 3, the thickness of the nut member 2 can be reduced. , that is, the difference between the inner diameter and outer shape of the nut member 2, if the outer diameter of the spline shaft 1 and the diameter of the ball 3 used are the same, the diameter of the nut member 2 can be reduced. In addition, if the outer diameter of the nut member 2 is considered as a reference, the outer diameter of the spline shaft 1 can be increased at a portion where the thickness of the nut member 2 can be reduced, and the allowable load of the ball spline device can be achieved. , Rigidity and so on. the

In addition, since the above-mentioned ball guiding surface 11 is formed along the tangential direction of the arc-shaped ball rolling groove 10, and smoothly continues with such a ball rolling groove 10, the balls 3 rolling in the ball rolling groove 10 can be moved by the ball rolling groove 10. The deflection groove 33 changes its traveling direction forcibly, and it can also be separated from the ball rolling groove 10 and transferred to the ball guiding surface 11 without jamming, so that the balls between the load straight groove 31 and the ball deflection groove 33 can be carried out smoothly. 3 contacts. Thus, in the ball spline device of the present invention, the infinite circulation of the balls 3 in the track groove 30 can be performed more smoothly. the

In addition, considering the smoother infinite circulation of the balls 3 in the track groove 30, it is preferable to form a smooth continuous surface without a boundary at the connection portion between the ball guiding surface 11 and the outer peripheral surface 12 of the spline shaft 1. the

Claims (4)

1. a ball spline device is characterized in that,

Constitute by splined shaft (1) and nut member (2), above-mentioned splined shaft (1) has axially formed ball rolling groove (10a, 10b) in the outer circumferential face upper edge, above-mentioned nut member (2) is formed roughly cylindric that this splined shaft (1) connects, be assembled on the above-mentioned splined shaft (1) through a plurality of balls (3), simultaneously, on the inner peripheral surface of facing with above-mentioned splined shaft (1), have above-mentioned ball (3) and carry out circuit rail slot (30)

Above-mentioned rail slot (30) is made of load straight-line groove (31), zero load straight-line groove (32), a pair of ball deflection groove (33), above-mentioned load straight-line groove (31) is the load straight-line groove that the ball rolling groove (10a, 10b) with splined shaft (1) forms opposite to each other, forms the load path of this ball; Above-mentioned zero load straight-line groove (32) is provided with abreast with this load straight-line groove (31), and is simultaneously, open towards the outer circumferential face of splined shaft (1); Above-mentioned a pair of ball deflection groove (33) links these load straight-line groove (31) and zero load straight-line grooves (32) communicatively, makes ball (3) contact between them, simultaneously, open to the outer circumferential face of above-mentioned splined shaft (1),

Above-mentioned ball deflection groove (33) makes the change in travel direction of the ball (3) that rolls forcibly in the ball rolling groove of above-mentioned splined shaft (1), utilize the profile of above-mentioned splined shaft (1) to make ball (3) break away from above-mentioned ball rolling groove (10a, 10b), on the other hand, jointly the ball (3) that breaks away from is induced to above-mentioned zero load straight-line groove (32) with the outer circumferential face of above-mentioned splined shaft (1)

Side at the ball rolling groove (10a, 10b) of above-mentioned splined shaft (1), with the ball of above-mentioned nut member (2) deflection groove (33) position in opposite directions on formed ball and induced face (11), this ball induces face (11) and ball rolling groove (10a, 10b) continuous sleekly.

2. ball spline device as claimed in claim 1, it is characterized in that, formed 2 ball rolling grooves (10a, 10b) for a pair of even number bar on above-mentioned splined shaft (1), the shape of each ball rolling groove in its cross section vertical with length direction constituted circular-arc.

3. ball spline device as claimed in claim 1, it is characterized in that a pair of end cap (5) that above-mentioned nut member (2) is fixed on by the nut main body (4) that has formed above-mentioned load straight-line groove (31) and zero load straight-line groove (32), when forming above-mentioned ball deflection groove (33) on the axial two end part of above-mentioned nut main body (4) constitutes.

4. ball spline device as claimed in claim 1 is characterized in that, above-mentioned nut member (2) is made of solid memder, has formed above-mentioned rail slot (30) within it on the side face.

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